The present invention relates generally to low voltage, high current electrical power distribution systems, and more particularly to a fused electrical disconnect device for use in a low voltage, high current electrical power distribution system.
Power distribution systems, such as telephone switching offices in telecommunications systems are often constructed on a large scale to serve many customers. Since telephone communications are essential for most businesses, it is necessary to ensure that telecommunications systems of this nature are highly reliable. To keep telecommunications systems operational in the event of power interruptions, most telecommunications systems typically include a plurality of high-capacity storage batteries to provide electrical power for operating telecommunications equipment whenever power from the conventional power sources becomes unavailable.
In these telecommunications systems, batteries and power converters are usually connected together so that operating telecommunications equipment are supplied with power from a collection of sources. Notwithstanding this, it is desirable to be capable of isolating individual pieces of telecommunications equipment (or small groups thereof) from the power sources in order to perform maintenance and installation activities. It is also desirable to provide overload protection for telecommunications equipment on an individual basis.
In large telecommunications installations, power distribution is arrayed with larger fused electrical disconnect devices installed in power distribution panels distributing power to smaller fused electrical disconnect devices installed in power distribution panels. Until recently, large fused electrical disconnect devices used in these telecommunications installations typically had a maximum current rating of about 800 amps. However, newer telecommunications installations have extended maximum current ratings for larger fused electrical disconnect devices up to about 1200 amps.
The smaller fused electrical disconnect devices used in telecommunications installations are typically connected to a power distribution panel that interconnects a power source supply buss and the load telecommunications equipment and include replaceable load protection fuses that interrupt power when an overload or fault condition exists. When an overload or fault condition occurs and the load protection fuse in a fused electrical disconnect device blows, the load protection fuse must be removed from the fused electrical disconnect device and replaced before current flow to the telecommunications equipment can be resumed.
Since the power distribution panels are supplied with power from batteries and other low-impedance sources, extremely high currents in the range of from about 10,000 to 100,000 amps can occur in the event of an overload or fault condition. Installing fused electrical disconnect devices from the rear of the power distribution panels can therefore be highly dangerous since there is a possibility that a conductive tool or part may come into contact with the power distribution panels and cause a fault. As a result, fused electrical disconnect devices that are installed into the front of a power distribution panel are preferred.
Fused electrical disconnect devices that provide an alarm signal whenever the load protection fuses therein blow have been considered. An example of a fused electrical disconnect device of this nature is described in U.S. Pat. No. 5,355,274 to Marach et al. However, these fused electrical disconnect devices have been limited to low voltage, low current applications. Knowing when a load protection fuse blows anywhere in an arrayed power distribution system is important.
It is therefore an object of the present invention to provide a novel low voltage, high current, fused electrical disconnect device.
According to one aspect of the present invention there is provided a fused electrical disconnect device comprising:
a housing defining a cartridge receptacle and including a line interface and a load interface within said receptacle;
a line terminal extending into said body and being in electrical communication with said line interface;
a load terminal extending into said body and being in electrical communication with said load interface;
a fuse holding cartridge removably insertable into said cartridge receptacle and releasably accommodating a load protection fuse, said fuse holding cartridge establishing an electrical current path between said line and load interfaces when said fuse holding cartridge accommodates a load protection fuse and is inserted into said cartridge receptacle; and
an alarm signal circuit in electrical communication with said line and load terminals, said alarm signal circuit generating an alarm signal when said electrical current path is interrupted and said line and load terminals are electrically coupled to a power source and load respectively.
Preferably, the alarm signal circuit also generates the alarm signal when the fuse holding cartridge is removed form the cartridge receptacle and the line and load terminals are electrically coupled to the power source and load respectively. In a preferred embodiment, the alarm signal circuit includes an alarm fuse in parallel with the load protection fuse. The alarm fuse electrically couples the line terminal to an alarm terminal when the load protection fuse fails to complete the electrical current path thereby to generate the alarm signal.
Preferably, the load protection fuse has a current rating in the range of from about 70 to 1200 amps. It is also preferred that the fuse holding cartridge includes a pair of resilient spring elements to engage the line and load interfaces thereby to retain the fuse holding cartridge in the cartridge receptacle.
According to another aspect of the present invention there is provided a low voltage, high current fused electrical disconnect device comprising:
a housing defining a cartridge receptacle and including electrically conductive, laterally spaced line and load interfaces within said receptacle;
generally cylindrical, laterally spaced line and load terminals extending from said housing, said line terminal being electrically coupled to said line interface and said load terminal being electrically coupled to said load interface;
a fuse holding cartridge removably insertable into said receptacle and releasably accommodating a load protection fuse, said fuse holding cartridge establishing an electrical current path between said line and load interfaces when said fuse holding cartridge accommodates a load protection fuse and said fuse holding cartridge is inserted into said receptacle; and
an alarm signal circuit in electrical communication with said line and load terminals, said alarm signal circuit generating an alarm signal when said electrical current path is interrupted and said line and load terminals are electrically coupled to a power source and load respectively.
The present invention provides advantages in that the fused electrical disconnect device generates an alarm signal whenever power to the load terminal is interrupted. Power interruption can be a result of a blown load protection fuse within the fused electrical disconnect device or the removal of the fuse holding cartridge from the fuse holding cartridge receptacle. Since the fused electrical disconnect provides an alarm signal when the fuse holding cartridge is removed from the fuse holding cartridge receptacle, situations where the fuse holding cartridge has been removed from the fuse holding cartridge receptacle but not replaced can be detected.
The present invention also provides advantages in that the fused electrical disconnect device is fully compatible with a range of class type fuses while maintaining a dimension similar to that of a conventional 600 amp fused electrical disconnect device.